Initiatorless Electric Detonator

ABSTRACT

The present invention relates to an electric detonator containing no primary charge or igniting charge, having a simple structure, and capable of directly igniting a base charge of secondary explosive. A detonator of the present invention includes a cylindrical tube closed at one end, a base charge contained in the tube near the closed end thereof, and an ignition device inserted from an open end of the tube and accommodated near the open end. The ignition device is a semiconductor bridge device including a laminate layer and electrode pads. The laminate layer includes layers of a reactive metal and a reactive insulator. The base charge is, for example, pentaerythritol tetranitrate.

TECHNICAL FIELD

The present invention relates to electric detonators, and specifically to electric detonators containing no primary charge.

BACKGROUND ART

A conventional instantaneous electric detonator includes a metal tube containing a primary charge (primary explosive) and a base charge (secondary explosive), an igniting charge, an electrical ignition device, a plug hermetically sealing the detonator, and conductive leg wires. Examples of the primary explosive include lead azide, diazodinitrophenol (DDNP), and lead trinitroresorcinate (tricinate). Examples of the secondary explosive include pentaerythritol tetranitrate (PETN), cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), and cyclo-1,3,5,7-tetramethylene-2,4,6,8-tetranitramine (HMX). The igniting charge used is, for example, a mixture of the primary charge and an oxidizing agent.

In the operational flow of the instantaneous electric detonator, a bridge wire (for example, a platinum wire or a nichrome wire) of the electrical ignition device is heated by supplying a current through the leg wires to ignite the igniting charge, which in turn ignites and explodes the primary charge, thus exploding the base charge. The base charge of the secondary explosive does not normally explode without a high energy as produced by the explosion of the primary charge of the primary explosive. The igniting charge and the primary charge, however, must be carefully handled during the production and use thereof because they are extremely sensitive to external stimuli such as heat, friction, and impact in comparison with the secondary explosive and general industrial explosives. To solve this problem, electric detonators containing no primary charge have been developed.

Patent Document 1 discloses a detonator containing no primary charge but containing a mixture of a secondary explosive and an oxidizing agent as a base charge. Specifically, the disclosed detonator is produced by charging and confining a mixture of PETN and potassium chlorate in an inner metal tube. This detonator functions without using a primary charge. However, a sensitive explosive such as an igniting charge is required for an ignition device for adding the base charge. In addition, the structure of the detonator is complicated because it requires a plurality of inner tubes.

Patent Document 2 discloses a method for detonating a base charge by applying impact using a flying plate. Specifically, a gas of a firing charge ignited by an igniting charge causes the flying plate to fly to and collide with the base charge, which is exploded by the collision energy. In this case, a sensitive explosive such as an igniting charge is used for an ignition device for causing the flying plate to fly. In addition, the structure of the detonator is complicated because it requires a structure for causing the flying plate to fly. Furthermore, the detonator can misfire if the flying plate is deformed by an adjacent hole on blasting and is therefore prevented from colliding properly with the base charge.

Semiconductor bridge devices, ignition devices based on semiconductor manufacturing technology, have been developed under the recent advance of electronic materials technology. As is well known, semiconductor bridge devices have higher efficiency and higher safety against electrical noise than conventional platinum or nichrome bridge wires (Patent Document 3).

Known semiconductor bridge devices for military applications detonate an explosive by applying a high voltage, although such high voltage application is unsuitable for ignition devices of detonators for industrial explosives. Also, a semiconductor bridge device disclosed in Patent Document 3, for example, is unsuitable for ignition devices of detonators for industrial explosives because of its low ignition energy.

-   Patent Document 1: Japanese Unexamined Patent Application     Publication No. 6-221799 -   Patent Document 2: Japanese Unexamined Patent Application     Publication No. 6-249594 -   Patent Document 3: Japanese Unexamined Patent Application     Publication No. 2004-513319

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

Accordingly, a complicated structure and increased production costs result if no primary charge is used. In addition, a sensitive explosive such as an igniting charge must be carefully handled during the production and use thereof. An object of the present invention is to provide an electric detonator containing no primary charge or igniting charge, having a simple structure, and capable of directly igniting a base charge of secondary explosive.

Means for Solving the Problems

As a result of intensive studies to solve the above problems, the inventors have found that the use of PETN or a mixture of PETN and a predetermined substance as a base charge, namely, a secondary explosive, and a semiconductor bridge (SCB) device as an ignition device eliminates the need to use a primary charge, thus enabling direct ignition of the base charge with a simpler structure.

That is, the present invention provides a detonator including a cylindrical tube closed at one end, a base charge contained in the tube near the closed end thereof, and an ignition device inserted from an open end of the tube and accommodated near the open end.

The ignition device is a semiconductor bridge device including a laminate layer and electrode pads. The laminate layer constitutes two lands on a substrate and a bridge portion electrically connecting the two lands. The laminate layer includes alternately stacked layers of a reactive metal and a reactive insulator. The electrode pads are electrically connected to at least one reactive metal layer of the laminate layer on the two lands thereof. The electrode pads allow an applied current of a predetermined intensity to flow through the bridge portion, thereby generating plasma.

The base charge contains pentaerythritol tetranitrate or pentaerythritol tetranitrate and at least one substance selected from the group consisting of metals, metal oxides, metal peroxides, metal nitrates, metal chlorates, and metal perchlorates. The inventors have found that the semiconductor bridge device, which is conventionally thought to be unsuitable as an ignition device for detonators of industrial explosives, can ignite the base charge without using an igniting charge or a primary charge.

In the detonator of the present invention, a metal oxide may be used instead of the reactive insulator. Using the metal oxide, the laminate layer can be more easily formed. In addition, the base charge can be ignited with a lower energy (lower current), so that the detonator can deliver high performance even if the resistance of the bridge portion is increased. This increases the number of detonators that can be connected to a single power supply.

The laminate layer includes the alternately stacked layers of the reactive metal and the reactive insulator or the metal oxide and generates plasma when a current flows through the metal pads electrically connected to the reactive metal layer. The reactive metal layer electrically connected to the metal pads is preferably the topmost layer of the laminate layer. This structure provides higher ignition efficiency.

In particular, if the reactive metal is titanium, tungsten, zirconium, or nickel, the detonator can be more easily produced and also has higher ignition efficiency. In addition, the reactive insulator is preferably boron, and the metal oxide is preferably SiO₂ or TiO₂. In such cases, the detonator can stably generate plasma.

The base charge used is preferably a combination of pentaerythritol tetranitrate and a metal. This combination provides higher ignition efficiency. In particular, nickel, tungsten, titanium, or aluminum is preferably used as the metal because they are easy to handle.

Advantages

The detonator of the present invention allows the semiconductor bridge device to directly ignite and explode a base charge of PETN without using a sensitive igniting charge. In addition, the detonator of the present invention has a simpler structure than known detonators containing no primary charge and delivers performance sufficient to detonate an industrial water gel/slurry and emulsion explosive. If the detonator of the present invention uses a PETN mixture, the mixture can be ignited with a lower energy than PETN alone.

BRIEF DESCRIPTION OF THE DRAWINGS

“FIG. 1” is a plan view of a semiconductor bridge device.

“FIG. 2” is a sectional view of the semiconductor bridge device taken along line A-A′.

“FIG. 3” is an enlarged view of a laminate layer 20.

“FIG. 4” is a sectional view of a detonator of Examples 2 to 4 containing no primary charge.

“FIG. 5” is a sectional view of a detonator of Example 1 containing no primary charge.

REFERENCE NUMERALS

100 semiconductor bridge device

10 silicon substrate

20 laminate layer

22-1 to 22-5 titanium layer

24-1 to 24-5 boron layer

30 and 32 land

34 electrode pad

36 bridge portion

1 tube

2 semiconductor bridge device

3 plug

4 base charge

5 leg wire

6 epoxy resin

7 stainless steel tube

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail.

A detonator of the present invention does not use a sensitive explosive used as an igniting charge or a primary charge for general electric detonators.

The detonator of the present invention uses PETN as a base charge. The PETN used may be of a grade generally used for detonators and is not limited in terms of, for example, purity.

Although PETN can be used alone, another substance for increasing the sensitivity of the base charge is preferably used in combination so that the base charge can be ignited with a lower energy. Examples of such an additive include metals such as titanium, tungsten, nickel, cobalt, iron, zinc, copper, and aluminum; metal oxides such as copper oxide; metal peroxides such as barium peroxide; metal nitrates such as sodium nitrate, potassium nitrate, and barium nitrate; metal chlorates such as potassium chlorate; and metal perchlorates such as potassium perchlorate. Among them, nickel, tungsten, titanium, and aluminum are preferred in terms of sensitivity.

A mixture of PETN and the additive (hereinafter referred to as a PETN mixture) is prepared by dissolving them in a solvent to form a slurry and sufficiently mixing and drying the slurry. The slurry can be dried by any method capable of removing the solvent. For example, the drying is performed at room temperature to 50° C. for one or more days. The solvent used can be water or an alcohol such as methyl alcohol or ethyl alcohol. The amount of solvent used may be about 50% to 200% by weight of the total weight of the PETN mixture.

The additive is used in such a proportion that it does not impair the power of PETN as an explosive, generally about 0.1 to 50 parts by weight, preferably about 1 to 10 parts by weight, based on 100 parts by weight of PETN. The PETN used preferably has an average particle size of 50 μm or less, more preferably 3 to 20 μm, so that it can be ignited with an energy produced by a semiconductor bridge device and can also provide a sharp, accelerating increase in burning rate. A PETN having an average particle size within such a range can be prepared by, for example, a recrystallization method as discussed on Page 310 of “CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES VOLUME 4”. The additive, on the other hand, preferably has an average particle size of 0.1 to 100 μm, more preferably 1 to 50 μm, in terms of the ignition sensitivity and manufacturing issues of the PETN mixture.

A binder may be optionally added to the PETN mixture to increase ease of handling and workability. Examples of the binder include rubbers such as fluorocarbon rubber, fibers such as nitrocellulose and ethylcellulose, and polymers such as poly(vinyl alcohol). The binder is dissolved in a solvent in which the binder is soluble (for example, acetone or water) and is added to the slurry containing the PETN mixture and the solvent such as water or an alcohol before the slurry is mixed and dried. It is generally preferred that the binder be added in a smaller amount, typically 5% by weight or less, more preferably 1% by weight or less, of the weight of the PETN mixture. The binder can be used for the same purpose if PETN is used alone. In this case, a solution of the binder in a predetermined solvent may be added to a slurry containing PETN and a solvent such as water or an alcohol before the slurry is dried. The binder solution, PETN, and the solvent may be added in any order and may also be simultaneously added if they can be homogeneously mixed. Similarly, in this case, it is generally preferred that the binder be added in a smaller amount, typically 5% by weight or less, more preferably 1% by weight or less, of the weight of PETN.

A semiconductor bridge device is used as the ignition device. FIG. 1 shows the semiconductor bridge device used in the present invention. FIG. 2( a) is a sectional view taken along line A-A′ of FIG. 1. FIG. 2( b) shows the structure of a laminate layer 20. A semiconductor bridge device 100 includes the laminate layer 20 and electrode pads 34 on a substrate 10. The laminate layer 20 constitutes two lands 30 and 32 and a bridge portion 36 connecting the two lands 30 and 32. The laminate layer 20 includes alternately stacked layers of a reactive metal and a reactive insulator or a metal oxide. The two lands are electrically connected to leg wires via the respective electrode pads 34, which are connected to at least one reactive metal layer of the laminate layer on the two lands thereof. The electrode pads 34 allow an applied current of a predetermined intensity to flow through the bridge portion, thereby generating plasma. For example, devices disclosed in Patent Document 3 and Japanese Patent Application No. 2004-290993 can be used. The semiconductor bridge device is used by connecting the electrode pads to the leg wires by wire bonding or using a conductive paste or a solder. In the present invention, the term “plasma” means a spark-like heat medium generated by a current flowing through the bridge portion.

Reactive metal layers 22-1 to 22-6 shown in FIG. 2( b) can be formed of, for example, gold, aluminum, silver, bismuth, carbon, cobalt, chromium, copper, iron, germanium, hafnium, indium, iridium, magnesium, molybdenum, niobium, nickel, lead, platinum, n-type silicon, p-type silicon, tin, tantalum, titanium, vanadium, tungsten, zinc, or zirconium. Among them, titanium, tungsten, zirconium, and nickel are preferred. Reactive insulator layers 24-1 to 24-5 are formed of a material that exhibits high chemical reactivity in combination with metals and has higher resistivity and lower thermal conductivity than metals. Examples of such a reactive insulator include boron, calcium, manganese, and silicon. Among them, boron is preferred. The layers 24-1 to 24-5 can also be metal oxide layers formed of, for example, SiO₂, TiO₂, or Al₂O₃ Among them, SiO₂ and TiO₂ are preferred.

At least one of the reactive metal layers 22-1 to 22-6 of the laminate layer 20 is electrically connected to the electrode pads 34. Preferably, as shown in FIG. 2( a), the topmost reactive metal layer 22-6 is electrically connected to the electrode pads 34.

FIG. 3 shows an example of the present invention. In this example, a tube 1 can be formed of a metal generally used for tubes of electric detonators, for example, copper, aluminum, iron, or stainless steel. The tube 1 is generally cylindrical, although the shape of the tube 1 is not limited to any particular shape. The inside and outside diameters, thickness, and length of the tube 1 can be appropriately determined according to applications and the amount of explosive. The tube 1 contains a base charge 4 of a secondary explosive. The base charge used is PETN or a PETN mixture. The amount of base charge used is generally 5 g or less, although it depends on the tube size and the desired charge density.

There is a general tendency that a higher charge density contributes to a higher power and a lower charge density contributes to a higher ignition sensitivity. For semiconductor bridge devices, however, a relatively high charge density contributes to increased ease of ignition. In the present invention, the charge density of the base charge is generally 1.0 g/cm³ or more, preferably 1.3 g/cm³ or more. The base charge can also be contained such that the charge density is decreased stepwise from near the semiconductor bridge device or such that the charge density is initially decreased and then increased again in terms of ignition sensitivity.

The PETN or PETN mixture used for the base charge 4 can be charged alone or as two or more layers. For example, the base charge 4 can include a lower PETN layer and an upper PETN mixture layer adjacent to the semiconductor bridge device.

A plug 3 equipped with a semiconductor bridge device 2 is inserted into the tube 1. The semiconductor bridge device 2 is electrically connected to leg wires 5. The plug can be formed of any material, such as a metal or a resin, that can withstand explosion pressure. After the insertion of the plug, the tube may be sealed using epoxy resin or by welding, for example, to increase sealing strength, or the top end of the tube may be crimped.

EXAMPLES

The present invention will be described in more detail with reference to the examples below, although the invention is not limited to these examples.

Example 1

As a base charge 2, 2.0 g of recrystallized PETN (having an average particle size of about 10 μm according to visual observation) was charged into a cylindrical copper tube 1 closed at one end and having an outside diameter of 8 mm, a thickness of 0.8 mm, and a length of 50 mm to a charge density of 1.5 g/cm³. A plug 3 equipped with a semiconductor bridge device was pressed into the tube 1 containing the base charge 4 such that the semiconductor bridge device came into contact with the PETN. For increased hermeticity, the top of the tube 1 was covered with a stainless steel tube 7 having an outside diameter of 9.5 mm and a thickness of 0.5 mm and was sealed with an epoxy resin 6. A detonator of the present invention was thus produced (FIG. 4). The semiconductor bridge device used included a silicon substrate 10, as shown in FIG. 1, with a size of 2 mm×2 mm and titanium layers (22-6 (1.0 μm), 22-5 (0.25 μm), 22-4 (0.25 μm), 22-3 (0.25 μm), 22-2 (0.25 μm), and 22-1 (0.05 μm)) and boron layers (24-5 (0.225 μm), 24-4 (0.225 μm), 24-3 (0.225 μm), 24-2 (0.225 μm), and 24-1 (1.0 μm)) stacked on the silicon substrate 10.

Example 2

A base charge was prepared by mixing 100 parts by weight of recrystallized PETN (having an average particle size of about 10 μm according to visual observation), 2.5 parts by weight of a 20% by weight acetone solution of fluorocarbon rubber, as a binder, and 100 parts by weight of ethyl alcohol and drying the mixture at 40° C. for one day. Then, 120 mg of the base charge was charged into a stainless steel tube 1 having an outside diameter of 8 mm, a thickness of 0.4 mm, and a length of 6 mm to a charge density of 1.5 g/cm³. The same plug 3 equipped with the semiconductor bridge device 2 as used in Example 1 was pressed into the tube 1 containing the base charge 4 such that the bridge device 2 came into contact with the base charge 4. A detonator of the present invention was thus produced (FIG. 3).

Example 3

A base charge was prepared by mixing 95 parts by weight of recrystallized PETN (having an average particle size of about 10 pm according to visual observation), 5 parts by weight of tungsten, 2.5 parts by weight of a 20% by weight acetone solution of fluorocarbon rubber, and 100 parts by weight of ethyl alcohol and drying the mixture at 40° C. for one day. Then, 120 mg of the base charge was charged into a stainless steel tube 1 having an outside diameter of 8 mm, a thickness of 0.4 mm, and a length of 6 mm to a charge density of 1.5 g/cm³. The same plug 3 equipped with the semiconductor bridge device 2 as used in Example 1 was pressed into the tube 1 containing the base charge 4 such that the bridge device 2 came into contact with the base charge 4. A detonator of the present invention was thus produced (FIG. 3).

Example 4

A base charge was prepared by mixing 95 parts by weight of recrystallized PETN (having an average particle size of about 10 μm according to visual observation), 5 parts by weight of aluminum (P-100, manufactured by Toyo Aluminum K.K.), 2.5 parts by weight of a 20% by weight acetone solution of fluorocarbon rubber, and 100 parts by weight of ethyl alcohol and drying the mixture at 40° C. for one day. Then, 120 mg of the base charge was charged into a stainless steel tube 1 having an outside diameter of 8 mm, a thickness of 0.4 mm, and a length of 6 mm to a charge density of 1.5 g/cm³. The same plug 3 equipped with the semiconductor bridge device 2 as used in Example 1 was pressed into the tube 1 containing the base charge 4 such that the bridge device 2 came into contact with the base charge 4. A detonator of the present invention was thus produced (FIG. 3).

Test Example 1

The detonator produced in Example 1 was inserted into 50 g of a water emulsion explosive (trade name: Ultex, manufactured by Nippon Kayaku Co., Ltd.). The detonator detonated the water emulsion explosive when supplied with an electrical energy of 3 J.

Test Example 2

The detonator produced in Example 2 was tested as in Example 1 by supplying different electrical energies to the semiconductor bridge device to count the number of times of ignition of the water emulsion explosive. Table 1 shows the test results.

TABLE 1 Number of times of ignition/ Energy (J) number of tests   3 J 2/2 0.8 J 34/37 0.5 J 13/28 0.3 J 0/6

Test Example 3

The detonators produced in Examples 3 and 4 were tested as in Example 1 by supplying an energy of 0.3 J to the semiconductor bridge device. As a result, both detonators detonated the water emulsion explosive.

According to the results of the test examples, the detonators of the present invention allow a semiconductor bridge device to directly ignite a base charge of secondary explosive and have performance sufficient to detonate an industrial water emulsion explosive. 

1. A detonator comprising a cylindrical tube closed at one end, a base charge contained in the tube near the closed end thereof, and an ignition device inserted from an open end of the tube and accommodated near the open end, wherein the ignition device is a semiconductor bridge device including a laminate layer and electrode pads, the laminate layer constituting two lands on a substrate and a bridge portion electrically connecting the two lands, the laminate layer comprising alternately stacked layers of a reactive metal and a reactive insulator, the electrode pads being electrically connected to at least one reactive metal layer of the laminate layer on the two lands thereof, the electrode pads allowing an applied current of a predetermined intensity to flow through the bridge portion, thereby generating plasma; and the base charge comprises pentaerythritol tetranitrate or pentaerythritol tetranitrate and at least one substance selected from the group consisting of metals, metal oxides, metal peroxides, metal nitrates, metal chlorates, and metal perchlorates.
 2. A detonator comprising a cylindrical tube closed at one end, a base charge contained in the tube near the closed end thereof, and an ignition device inserted from an open end of the tube and accommodated near the open end, wherein the ignition device is a semiconductor bridge device including a laminate layer and electrode pads, the laminate layer constituting two lands on a substrate and a bridge portion electrically connecting the two lands, the laminate layer comprising alternately stacked layers of a reactive metal and a metal oxide, the electrode pads being electrically connected to at least one reactive metal layer of the laminate layer on the two lands thereof, the electrode pads allowing an applied current of a predetermined intensity to flow through the bridge portion, thereby generating plasma; and the base charge comprises pentaerythritol tetranitrate or pentaerythritol tetranitrate and at least one substance selected from the group consisting of metals, metal oxides, metal peroxides, metal nitrates, metal chlorates, and metal perchlorates.
 3. The detonator according to claim 1 or 2, wherein the reactive metal layer electrically connected to the electrode pads is the topmost layer of the laminate layer.
 4. The detonator according to claim 1 or 2, wherein the reactive metal is titanium, tungsten, zirconium, or nickel.
 5. The detonator according to claim 1, wherein the reactive insulator is boron.
 6. The detonator according to claim 2, wherein the metal oxide is SiO₂ or TiO₂.
 7. The detonator according to claim 1 or 2, wherein the base charge comprises pentaerythritol tetranitrate and a metal.
 8. The detonator according to claim 7, wherein the metal is nickel, tungsten, titanium, or aluminum. 